Fuel consumption of an engine may vary as operating conditions of the engine change. For example, fuel consumption may be affected by engine speed, load, and fuel injection parameters such as injection timing and injection amount. By knowing the fuel consumption during vehicle operation, driving may be performed more efficiently, for example, such that fuel economy is increased. In one example, real-time fuel consumption is estimated by integrating fuel quantity injected over time (e.g., a control system's estimate of fuel quantity injected per cycle multiplied by engine speed). If the control system's estimate of fuel quantity injected is not accurate, however, the fuel consumption estimate may not be accurate either. In another example, a fuel flow meter is added to the system; however, this increases a number of parts and cost of the system.